1. Field of the Invention
The present invention relates to an immersion evaporator having a pipe connected to an evaporation vessel, for feeding the solution to be treated into the evaporation vessel, a riser pipe for removing the concentrated solution and any crystals from the evaporation vessel, a pipe for removing flue gases and vapors from the evaporation vessel, and an immersion pipe extending substantially vertically inside the evaporation vessel, for directing hot flue gases below the surface of the solution in the evaporation vessel.
2. Description of the Prior Art
The term immersion evaporator denotes a device in which hot flue gases are directed below the surface of the liquid to be evaporated.
In direct emmersion evaporation, the flue gases discharging from the immersion pipe are allowed to bubble through the solution. In this manner it is possible to produce a highly effective transfer of heat and material from the flue gases into the liquid being treated. Since heat exchangers are not required, the question of material do not cause problems. For this reason, direct immersion evaporators are used, especially in metallurgical and chemical processes in which corroding conditions cause problems in material selection, for example, in the heating and evaporation of strongly acidic solutions.
In immersion evaporators, the immersion pipe is usually installed in a vertical position in order to minimize the amount of material which comes into direct contact with the liquid to be treated.
Previously known are numerous different immersion evaporators. In these evaporators, the objective has usually been an apparatus of minimum possible size in order to reduce the investment coast. The reducing of the apparatus size, however, causes a decrease in the volume of flue gases prior to the discharge point, and in this case even slight variations in the feed of fuel or combustion gas cause great variations of pressure in the immersion pipe. For this reason, rather complicated immersion pipe structures, with all the involved problems, have been developed.
Aiming at a small size is also disadvantageous for the reason that the detrimental thermal effect of combustion per one surface unit of the apparatus increases, and thereby the quality and endurance of the material are put to a hard test.
In general, the combustion chamber is installed directly above the immersion pipe, as its continuation, and it bears on the structures of the treatment vessel. This arrangement has certain drawbacks. First, with high capacities it is necessary either to reduce proportionately the size of the combustion chamber, thereby causing load problems, or to enlarge the evaporation vessel unnecessarily so as to be able to fit the combustion chamber above it. Secondly, the vibrations occurring in the combustion chamber and the immersion pipe, and any liquid drops splashing in it (cf. U.S. Pat. No. 3,276,443), have a detrimental effect on the lining of the furnace so that especially the horizontal vault of the combustion chamber is easily damaged and can collapse. Also, the entire combustion chamber must be detached during the maintenance of the immersion pipe.
However, from the publication Gas Varme International Bp 19, No. 6 (June 1970), page 229, an immersion evaporator is known in which the combustion chamber is in a horizontal position and connected to a vertical immersion pipe by means of a right-angled joint piece. In this structure, the size of the combustion chamber is independent of the size of the evaporation vessel, and the liquid drops splashing into the immersion pipe cannot affect the lining of the combustion chamber.
In an immersion evaporator according to the invention, the combustion chamber is provided with a burner for liquid or gaseous fuel, the burner having a cylindrical turbulence chamber for an oxygen-bearing combustion gas, there being at one end of the chamber a substantially tangential combustion gas inlet conduit and a fuel dispersion pipe extending coaxially into the turbulence chamber, in which case the opposite end of the turbulence chamber is convergent in order to increase the angular velocity of the combustion gas before the fuel discharging from the dispersion pipe is mixed with it.
In the immersion evaporator according to the invention, a burner is used by means of which the fuel and the oxygen-bearing combustion gas can be effectively mixed with each other, either in the burner or in the combustion chamber. The object is to provide an immersion evaporator in which a flow field is formed in front of the burner, the fuel and the oxygen-bearing combustion gas being mixed in this field rapidly and within a consistent velocity range so that the combustion proceeds to a certain stability field of the spray and stabilizes in this velocity field. A suitable velocity field can also be obtained by fitting a solid object in the spray. An area of a suitably low flow velocity is formed behind this object and the flame stabilizes there, as described in German Application Ser. No. 24 34 459.
U.S. Pat. No. 3,185,448 discloses a burner in which the fuel is sprayed into a toroidal turbulence formed from the combustion air. This turbulence is produced either by directing the combustion air into the combustion chamber from its opposite end or by means of baffling members extending into the combustion chamber.
Also previously known are burners in which the combustion gas is caused to revolve about its axis of travel, in which case centrifugal force spreads the spray so that its travel velocity is attenuated relatively rapidly in order to create a suitable velocity range for the combustion. A great number of turbulences with a mixing effect appear in such a spray.
In the burner according to German Application Ser. No. 21 33 126, the inlet for discharging combustion gas into the combustion chamber has the shape of a diverging cone having a throttling area with rounded corners. This is in order to direct the combustion gas spray so as to spread it relatively gently and to form an ignition field in the conical flare of the discharge opening.
Burners usually require safety devices and auxiliary devices, such as flame guards and ignition devices. Fitting these auxiliary devices in the burner often causes great difficulties. Often the auxiliary devices must be placed at a point where their useful life is short owing to the heat.
Furthermore, in several known burners, flame-baffling members are used which extend inside the combustion chamber and are thereby exposed to the flame, or structures are used which have a large opening via which the radiation of the combustion chamber and the flame can reach the inner parts of the burner.
The object of the present invention is therefore to provide an immersion evaporator provided with a burner of the type mentioned above; by means of this burner it is possible to obtain a very effective field of mixing using a very small discharge opening, from which a consistent and highly turbulent spray is obtained.
An object of the present invention is also to achieve an immersion evaporator, in which the turbulence of the oxygen containing burning gas is created by introducing the burning gases tangentially to the turbulence chamber. By the method the disadvantages are avoided that are encountered when turbulence is brought forth or fortified by the aid of conducting or auxiliary means, e.g. by baffles. In prior art burners the baffles used for the creation of turbulence have prevented the observation and an effective regulation of the burning.
The object of the present invention is in particular to provide an immersion evaporator, in which it is possible to burn heavy fuel oil, which has so far been found difficult to burn. The requirements to be set on the burner increase with decreased volatility of the fuel, i.e. approximately according to the flash point of the fuel. In order to achieve sufficient vaporization, the fuel must usually be atomized into very fine droplets, less than 100 micrometers, and in order to achieve this it has been necessary to heat the fuel oil to 370.degree. K. at minimum.